Transmission of painful sensations

The gate control theory describes pain transmission. The gate mechanism that alters the transmission of painful sensations from peripheral nerve fiber to the thalamus and cortex of the brain is located in the dorsal horn of the spinal cord. The thalamus and cortex of the brain are where the body recognizes painful sensations as pain. 

Stage I—analgesia Loss of pain sensation results from interference with sensory transmission in the spinothalamic tract. The patient is conscious and conversational. A reduced awareness of pain occurs as Stage II is approached. 

When either of the compounds is applied to the skin or mouth, a burning sensation results. This sensation is caused by the compounds bonding to receptors of small sensory neurons associated with the transmission of pain. Following repeated application of capsaicin or RTX, these neurons, or C sensory nerve fibers, become desensitized to the initial irritation or pain the compounds cause. This characteristic allows the compounds to be used topically to relieve chronic pain. Capsaicin is now used as an ingredient in a few OTC pain-reheving creams such as Capzasin-P, Meet, Menthacin, and Pain Doctor. 

Signals from pain receptors are transmitted to the brain where they are processed in the thalamus and then passed on to the sensory cortex where the sensation of pain originates. Receptors for endorphins (and for the opiates) are abundant in these regions and it is likely that a natural role of endorphins is to interfere with the transmission of impulses through these regions. The opiates appear to do the same, acting not so much to alter the pain threshold but altering the patient s attitude to pain. 

The nervous system consists of sensory and motor compo-nenLs. The. sensory compiment responds to various external stimulations, which it transmits in the form of a nerve impulse to the CNS for interpretation. The motor component of the nervous. system carries a signal from the CNS to the appropriate part of the bixly to elicit the rasponse to the stimulation. One of thc.se rcspoascs is the sensation known as pain. Nerve impulses arc now known to take the form of an electrical impulse. Experimental evidence suggests that both stimulation and the transmission of a nerve impulse may be bUx ked by the action of local anesthetic agents. Consequently, understanding this action requires a knowledge of the structure and action of the nervous system. 

Capsaicin achieves pain relief by depleting substance P from sensory neurons in the spine, thereby decreasing pain transmission. Capsaicin is not effective for acute pain up to 2 weeks may be necessary before pain relief is appreciated. Most patients experience a local burning sensation at the site of application. The discomfort usually does not result in... 

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